1. Field of the Invention
This invention relates generally to an apparatus and method for testing various diesel fuels and diesel fuel additives, and more particularly to an apparatus and method for quantitatively predicting the deposition characteristics of various diesel fuels and diesel fuel additives formed during operation of a diesel engine.
2. Description of Related Art
Heretofore it has been extremely difficult to provide test apparatus and methods that consistently provide reliable quantitative evaluations of the deposition and/or cleaning characteristics of various diesel fuels and diesel fuel additives. More importantly, it has been difficult to provide bench test results that correlate with the deposit characteristics experienced during actual engine operation. Often, because of the small surface area of a test component and the resultant short residence time that the test fuel is in contact with the component surface, in addition to environmental and control variables during testing, it has been very difficult to obtain consistent results in repeated bench tests.
For example, the test apparatus described in U.S. Pat. No. 5,693,874 issued Dec. 2, 1997 to Jose L. DeLaCruz, et al. for Test Apparatus and Method for Determining Deposit Formation Characteristics for Fuels, and assigned to the Assignee of the present invention, places a test piece having the shape characteristic of an engine valve in a test chamber. The exposed surface available for deposit formation comprises only a portion of the flanged head of the representative engine valve. As a result of the minimal surface area, i.e., the backswept portion of the valve head, the fuel to be tested is in contact with a relatively small deposition surface for only a very short time. Because of these inherent limitations, it has been necessary to run fuel deposition tests for extended periods of time in order to obtain sufficient weighable deposits, thus contributing to variances in deposition characteristics from test to test. In addition, the necessarily prolonged test periods lessen the sought-after advantage of relatively easy, relatively inexpensive tests to evaluate the deposition characteristics of different fuels and fuel additives.
Several attempts have been made to provide a diesel fuel test apparatus that will accurately and repeatedly produce accurate indications of the tendency for different fuels and fuel additives to form, or remove, deposits on or from fuel delivery and combustion chamber components of an internal combustion engine. In addition to the prior attempts discussed in the Background of the Invention section of the parent application, other test schemes propose distilling the fuel to reduce it in such a manner that the residual fuel includes only the higher viscosity fractions. The residual fuel is passed over a heated inclined ramp, and the flow distance along the ramp and the residual weight of the fuel measured. For example, see U.S. Pat. No. 3,108,468 granted Oct. 29, 1963 to B. L. Mickel for an Engine Fuel Test Device, and U.S. Pat. No. 5,036,699 granted Aug. 6, 1991 to Rolf Fikentscher, et al. for an Apparatus for Testing Fuel Additives and Oil Additives. In the devices described in those patents, and in the prior art in general, there are no teachings directed to the application of a test fuel composition and hot air to a heated substrate having an adequate surface area, distributed over a sufficient length, to enable one to quickly, accurately, and repeatedly assess the deposit removal characteristics of selected fuels and fuel additives.
Furthermore, test apparatus in current use require elastomeric seals to seal the test chamber and the fuel, air and other connections to the test chamber. Elastomeric seals deteriorate rapidly in the presence of heat, fuel and fuel additives, all of which are routinely encountered in diesel fuel testing. As a result of rapid deterioration, elastomeric seals have a very limited service life in hot fuel test environments and must be replaced at relatively short intervals.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a test apparatus that provides a substrate surface that has a surface area and flow length sufficient to provide adequate residence time for the tested fuel mixture to remain in contact with the substrate, and thereby quantitatively demonstrate the deposit forming or cleaning characteristics of the fuel mixture. It is also desirable to have a fuel test apparatus that does not rely on elastomeric seals to provide airtight seals between the various components of the test apparatus.
In accordance with one aspect of the present invention, a diesel fuel test apparatus has a substrate component disposed in a holding chamber. Importantly, the substrate component has a surface at least partially defined by at least one tortuous passageway. The test apparatus further includes a source of fuel selected from the group consisting of diesel fuel, diesel fuel additive substances, and mixtures of diesel fuel and diesel fuel additive substances, the source of fuel being in fluid communication with the holding chamber. Also, the test apparatus includes a source of heated air that is in fluid communication with the holding chamber.
In accordance with another aspect of the present invention, a method for evaluating the deposit forming characteristics of a candidate fuel includes weighing a substrate component having a surface at least partially defined by at least one tortuous passageway, and determining an initial weight of the substrate component. The weighed substrate is then placed in a holding chamber adapted to maintain at least a portion of the substrate component in intimate contact with an interior surface of the holding chamber. Subsequently, a test cycle is carried out that includes introducing a selected quantity of fuel into the holding chamber and onto the defined surface of the substrate component. A stream of air heated to a selected temperature is then passed through the holding chamber for a selected period of time. The introduction of fuel and the passing of heated air through the holding chamber is repeated throughout a number of cycles carried out over a selected period of time, after which the steps of the test cycle are discontinued. The substrate component is again weighed and the weight of the substrate component after discontinuing the test cycle is measured. The difference between the initial weight and the after-test weight of the substrate component is then calculated.